Optical waveguide components, such as couplers, of various constructions are well known and in widespread use, especially in the telecommunications field. Generally, optical waveguide couplers make it possible to interconnect individual optical waveguide fibers so that the modulated light propagating through an input optical fiber pigtail leading to the optical waveguide coupler continues to propagate through at least one output optical fiber pigtail leading from the optical waveguide coupler. In some optical waveguide couplers, at least two input optical waveguides are coupled within the optical waveguide coupler so that the output light signal is a combination of the input light signals. Examples of optical waveguide couplers are disclosed by U.S. Pat. No. 4,902,324 to Miller et al., U.S. Pat. No. 4,931,076 to Berkey, U.S. Pat. No. 4,948,217 to Keck et al., U.S. Pat. No. 4,943,130 to Dannoux et al., U.S. Pat. No. 5,009,692 to Miller et al., and U.S. Pat. No. 5,011,251 to Miller et al.
Generally, optical fibers used in coupler fabrication have a core, a cladding surrounding the core, and a coating around the cladding. Such fibers are treated to remove the coating (e.g., by mechanical stripping) where the coupling between the optical fibers is to be formed. In fabricating one type of coupler, called a multiclad fused taper coupler, the stripped portions of the optical fibers are positioned inside a hollow glass tube after being inserted into funnels formed at the ends of the glass tube. The central portion of the tube is then heated to collapse it around the optical fibers and drawn to create coupling between the two fibers. The tube thus includes a drawn region joining a pair of tapered regions each leading to a funnel. The optical fibers extend out of the coupler at wide ends of the funnels. The fibers themselves are tapered in the exit regions between the tapered regions and the funnels.
To strengthen the attachment of the optical fibers to the coupler tube, an adhesive is injected into the funnels at their wide ends to bond the optical fibers to the tube. A wide variety of adhesives can be utilized for this purpose. However, an ultraviolet radiation curable epoxy is preferred, because it can be cured rapidly, permitting more efficient manufacture of the coupler.
Other glass components utilize discrete optical fiber pigtails attached to a surface of the optical component with the end face of the optical fiber aligned with a corresponding optical waveguide output in the optical component (see, e.g. Dannoux et al. U.S. Pat. No. 4,943,130). For these components the adhesive may provide the only attachment between the optical component and the optical fiber pigtail.
Despite the preference for epoxy adhesives, optical components treated with this adhesive are still susceptible to adhesive delamination when exposed to humidity or dry thermal cycling. It is believed that such environmental conditions cause delamination due to disruption of the Vander-Waals forces which bond the epoxy to the glass surfaces of both the optical fibers and the coupler tube. The resulting weakened attachment of the optical fibers to the tube has the potential to affect adversely the coupler's performance. Thus, despite the use of adhesives, the need remains for a technique of firmly bonding the optical fibers to the component surface even under hot and/or humid conditions. This is especially true for multiclad couplers where the tapered fibers are susceptible to movement and breakage.
It is known in the art to include silane in the acrylate adhesive composition used to attach optical fibers to the surfaces of substrates with ion-exchanged optical waveguides incorporated therein. Such devices are described in Dannoux U.S. Pat. No. 4,943,130. Howevers, in some cases this method of altering the glue composition is not sufficient to ensure the attachment of the optical fibers to the substrate during environmental changes, especially in the presence of damp heat.